This invention relates to apparatus for providing a simulated night vision display and, more especially, this invention relates to apparatus for providing a simulated night vision display utilising night vision goggle means.
There are two currently known basic approaches for providing night vision goggle training in simulators such for example as flight simulators. The first basic approach uses simulation, and the second basic approach uses stimulation.
With the simulation approach, an instrument based on the actual issued night vision goggle means is used in conjunction with tracker means and a dedicated image generator. The tracker means is usually a 3 degrees of freedom tracker means. The tracker means determines the wearer""s attitude in space, which in turn is passed to an auxiliary image generator for providing simulated infrared night vision goggle images. These images are then passed to a miniature cathode ray tube display (visible green phosphor) housed in a dummy night vision goggle casing. The image generator data base must attempt to faithfully replicate the night vision goggle shortcomings such for example as blooming, noise, smear, and AGC effects. The image generator data base must also attempt to faithfully replicate the changed appearance of objects illuminated largely by infrared.
With the stimulation technique, actual out of the window imagery presented by the simulator visual is used to stimulate real night vision goggles. In order to do this, the simulator visual must be run at very low light levels, and a high degree of light tightening against stray illumination must be offered. Whilst this technique can be effective, using as it does actual night vision goggles, the data base must still be altered to give the correct appearance of objects seen largly with infrared. The imagery, although being presented by actual night vision goggles, does not fully represent actual conditions due to the fact that the night vision goggles are being illuminated by visible light only. The stimulation technique can only be used with simulator displays that can operate right down to cut off. This usually precludes any other form of display except cathode ray tube based displays. The degree of light tightening can be difficult to achieve and maintain. In addition, if the wearer looks around the night vision goggle oculars, a rather unconvincing night time image is seen, which is usually only red in colour.
In connection with the above mentioned basic simulation technique, it is also known to use miniature cathode ray tube displays to excite actual night vision goggles. However, this was done with visible light and the variation was rejected due to the size and weight of the cathode ray tube and its systems. With the above mentioned basic stimulation technique, some high end systems have used a fourth infrared cathode ray tube over and above the usual red, green and blue ones in order to stimulate the night vision goggles at infrared, and yet maintain a valid visible light image for direct view purposes. This has the disadvantage of requiring an extra image generator channel as well as extra cathode ray tubes.
None of the above mentioned approaches to effective night vision training are able to simulate the constant re-focusing required when night vision goggles are used near to the ground, or in air to air re-fuelling, when the very limited depth of field of night vision goggles becomes a major problem. In addition, none of the above mentioned basic approaches to night vision goggle training can readily address the dynamic range of the illumination presented to night vision goggles. This ranges from signals lost in inherent tube noise (less than starlight illumination) to almost daylight levels. It is under these conditions that many night vision goggle defects are exacerbated. The root cause of the lack of dynamic range stems from the typically eight bit (256 level) nature of the video signals from the image generator. Various schemes have been attempted to increase this lack of dynamic range, by using motorized neutral density filters or by re-using the redundant bloom channel, switched over in attenuated form to add to the red channel being used to stimulate the night vision goggles. These schemes have not been particularly successful.
It is an aim of the present invention to reduce the above mentioned problems.
Accordingly, the present invention provides apparatus for providing a simulated night vision goggle display, which apparatus comprises night vision goggle means giving night vision at night, reflective micro-display means for illuminating the night vision goggle means, tracker means for tracking the attitude of the night vision goggle means, and image generator means for providing infrared images to the night vision goggle means, the image generator means being such that it has a first channel which is used to drive the reflective micro-display means with a high level of illumination, a second channel which is used to drive the reflective micro-display means with a medium level of illumination, and a third channel which is used to drive the reflective micro-display means with a low level of illumination.
The apparatus may be one in which the reflective micro-display means is a ferroelectric liquid crystal display reflective micro-display means. The ferroelectric liquid crystal reflective micro-display means is preferably in the form of a panel. Reflective micro-display means other than the ferroelectric liquid crystal display reflective micro-display means may be employed if desired.
Usually, the tracker means will be a 3 degrees of freedom tracker. Such a tracker will normally be satisfactory for flight simulators. If desired, for example for other types of simulators, a full 6 degrees of freedom tracker may be used. Such a full 6 degrees of freedom tracker tracks both position and angle.
The apparatus may be one in which the first, second and third channels are each assigned to at least one light emitting diode, and in which the light emitting diodes for each of the first, second and third channels have progressively lower light outputs. The progressively lower light outputs may be achieved electrically, or with the use of neutral density filters.
The apparatus may be one in which the night vision goggle means has potentiometer focusing means for focusing the night vision goggle means. The potentiometer focusing means may be arranged to operate a mechanical focus wheel found in known night vision goggle means.
The night vision goggle means will usually be binocular. If desired however, the night vision goggle means may be monocular.